In recent years, integrated circuitry has become increasingly larger in its scale of integration, and manufacturing semiconductor boards of VLSI chips or the like has come to require super minute patterning capable of ensuring trace widths of half a micron or below. In order to meet this requirement, wavelengths of exposure apparatus used in photo-lithography have become shorter and shorter, and it is being considered now to utilize excimer laser beams of shorter wavelengths in the ultraviolet region (e.g., XeCl, KrF, ArF).
In forming patterns by lithography in such a wavelength region, chemical amplification resist is used to advantage.
In general, chemical amplification resist compositions fall roughly into three categories: the so-called 2-component, 2.5-component and 3-component systems. In the 2-component system, a compound capable of generating an acid by photolysis (referred to as a photo-acid generator, hereinafter) and a binder resin are used in combination. The binder resin used therein is a resin containing groups capable of decomposing under the action of an acid to increase the resin solubility in an alkali developer (acid-decomposable groups). In the 2.5-component system, a low molecular-weight compound having an acid-decomposable group is further included in addition to such a 2-component system. The 3-component system includes a photo-acid generator, an alkali-soluble resin and such an acid-decomposable compound of low molecular weight.
Although those chemical amplification resist compositions are suitable as photoresist compositions for ultraviolet or far-ultraviolet irradiation, it is further necessary for them to provide for characteristics required from the viewpoint of using them.
In the case of photoresist compositions designed for use of an ArF light source, there is a proposal to introduce alicyclic hydrocarbon moieties into resins for the purpose of providing dry etching resistance. However, the introduction of alicyclic hydrocarbon moieties renders the resin extremely hydrophobic, thereby yielding such a detriment that the photoresist is difficult to develop with an aqueous solution of tetramethylammonium hydroxide (abbreviated as TMAH hereinafter) hitherto widely used as a resist developing solution or peels off a substrate during development.
As a measure against the resin's hydrophobicity, mixing an organic solvent, such as isopropyl alcohol, into a developer was considered and met with a qualified success. However, the mixing with an organic solvent causes apprehension of swelling of resist films and makes the patterning process complex, so it cannot be always said that the problems have been solved. In an approach of improving resist, hydrophilic groups have frequently been introduced as a measure for complementing various hydrophobic alicyclic hydrocarbon moieties.
JP-A-9-73173 discloses the resist material using an acid-responsive compound that has an alkali-soluble group protected with an alicyclic group-containing structure and contains a structural unit capable of rendering the compound soluble in an alkali through elimination of the alkali-soluble group by an acid.
Further, JP-A-11-119434 offers the resist material using a resin having repeating units containing alicyclic hydrocarbons and repeating units having lactone structures as a low-cost resist material having high resolution, high sensitivity and improved dry etching resistance.
JP-A-2000-292917 discloses the resist composition using a mixture of an acid generator of triarylsulfonium salt type and an acid generator of phenacylsulfonium salt type.
In addition, JP-A-2001-294570 discloses the resist composition containing a phenacylsulfonium salt.
However, the hitherto known positive resist compositions do not produce satisfactory results on line edge roughness and pattern collapse performances in micro-photo fabrication using far ultraviolet light, notably ArF excimer laser beam.